This invention relates to a method of constructing unitary fiber reinforced resin composite containers using a vacuum assisted resin transfer molding process.
Fiber reinforced composite containers such as railcar bodies, intermodal containers, and truck bodies which incorporate materials such as foam and balsa cores are desirable because they are lightweight, corrosion resistance, and provide excellent thermal insulation. To make these containers competitive with metal structures, the manufacturing costs must be minimized without sacrificing structural performance. Typically, high stress levels are generated in the corners of these containers due to large bending moments. For applications such as railcar bodies, high compressive stresses in the floor are experienced due to fork lift truck wheel loading.
Composite containers can be produced in several ways. One method consists of assembling a series of flat panels (e.g., pultrusions) using a secondary adhesive bonding approach. This manufacturing approach results in joints at the corners of the structure and a discontinuity of fiber reinforcement. This invention eliminates fiber discontinuities at the corners and adhesive bonding of multiple panel sections.
Typically, composite parts and structures which are exposed to the environment need to be protected from UV degradation and weathering, as well as being made aesthetically pleasing. The effects of UV and weathering are currently reduced or eliminated by: incorporating UV absorbers into the resin; incorporating fillers into the resin; pigmenting the outer resin layers of the composite part; gel coating the surface prior to molding; and/or painting the finished surface. Of these methods, gel coats (which are applied prior to the composite fabrication process), and paint (which is applied as a secondary operation after the composite fabrication process) are the most effective. However, the application of gel coats or paints results in the emission of VOCs. Both gel coating and painting operations also require a large capital expenditure both in spraying and ventilation systems and equipment. Gel coated parts must be layed up and molded within a reasonable time after the gel coat is applied, in order to obtain a good bond between the gel coat and the part being molded. However, large, structural parts may take several days to lay up, many more during the prototyping stages. Automation and process improvements will speed up the lay-up time, but this time will probably still be too long for a gel coating operation. Aesthetically pleasing surfaces are usually accomplished by either gel coating or painting.
This invention defines an approach for constructing large composite containers using a vacuum assisted resin transfer molding process. The method is applied to large composite containers such as rail car bodies which may be as large as 68 feet long by 10 feet wide by 12 feet high. The approach consists of molding only two (2) individual parts which are subsequently joined. An open box with 2 or 4 sides and a floor is fabricated in one molding step with the top or roof molded in a separate operation.
The materials (e.g., fabric and cores) are initially positioned on three (3) or five (5) separate molds which are supported by casters and oriented horizontally. After the individual sections are laid-up, the two (2) sidewalls and optionally two (2) endwalls are attached to the base floor mold. The sidewalls and endwall molds are then rotated into a vertical position and bolted together. The hinging mechanism allows for the mold segments to be attached to the base mold and rotated freely into a vertical position. The hinge also provides for a secondary lateral movement to seat the sidewall molds to the base mold.
The sidewall and endwall molds are designed so that a small portion of the floor is included. This allows the entire corner geometry to be incorporated and creates a vertical joint with the floor mold. This section of the mold also provides a lip which effectively contains the lay-up during mold rotation. At the interfaces between molds, a seal is provided to maintain the vacuum integrity of the assembled mold because if air leaks along the mold, surface finish defects and possibly structurally weakened areas (depending on the intensity and location of the leak) will occur. Indexing keyways are also provided to ensure alignment between sections.
This invention relates to the material lay-up method used to maintain the fiber continuity across the corners of the composite container. Although the five sections are laid up separately, fiber continuity is maintained by the inclusion of additional material in each lay-up beyond the size of the section. This added material is initially folded back on itself and then unfolded after the molds are assembled. The layers of unfolded fabric extend the required distance and are interleaved (overlapped) with fabric in the adjacent section to effectively transfer the load around the corner.
Metal caul plates may be positioned over the inside of the lay-up to improve surface definition and smoothness. These caul plates are held in place by retainers at the top of each section to prevent movement during the rotation of the molds.
After the molds are assembled and the fabric is unfolded in each corner, the entire lay-up is vacuum bagged. A pre-seamed vacuum bag is used which replicates the inside of the box. A continuous seal is created at the top edge of the sidewalls and endwalls. A resin matrix is then infused into the box using a vacuum assisted resin transfer molding process. Once the resin has cured the box is now a unitary structure.
The sidewalls can have openings within the sidewalls of the size and shape suitable for accommodating structural elements, such as doors and windows, or suitable for the installation of miscellaneous systems and/or equipment, such as mechanical refrigeration units. The composite box can comprise means for supporting ancillary structures appendable to the composite box, such as metal attached plates, mounting studs/threaded attachments, bearing plates, brackets, beams, fittings, hinges, lateral beams, transverse beams, floor stringers, corner rails, and/or posts. The composite box can further integrate internal co-molded hollow elements integrated within the walls of the composite box suitable for running utilities, such as co-molded ducting and/or conduits for air flow, water, and miscellaneous systems, such as electrical wiring.
The method of forming a composite box having end, side, and bottom walls comprises forming a plurality of cores, each having a peripheral surface, length and width dimensions extending end-to-end and side-to-side, respectively, positioning said cores end-to-end and side-by-side in respective mold segments that define said end, side, and bottom walls while encapsulating the cores in fabric material; assembling the mold segments to interface with one another to form a box, said fabric material overlapping with fabric material in adjacent mold segments; sealing the interface between the mold segments enclosing said molds in a hermetically sealed bag having inlets and outlets; connecting a source of uncured resin to said inlets evacuating said molds through said outlets; forcing said uncured resin through said inlets to said outlets to fill the mold between said core and said mold to impregnate said fiber material; curing said resin to form a Composite box; and removing the mold segments. Preferably, the resin is vinyl ester or polyester.
In forming the composite box of the present invention, openings can be included within the walls of the composite box of a size and shape suitable for accommodating structural elements. The cores can be positioned in order to create an opening within the sidewalls suitable for accommodating structural elements. Means for supporting ancillary structures to the walls within the composite box can be appended to the walls of the composite box. Hollow elements having endings at the surface of the walls of the composite box can be co-molded within the composite box, and the endings of the hollow elements can be filled with an easily-removable substance, such as clay, preventing the hollow openings from filling with resin during the process of filling the molds.
The composite box structure comprises end, side, and bottom walls, each of said walls, including a plurality of cores having a peripheral surface, length and width dimensions; the cores are positioned end-to-end and side-by-side to define said end, side, and bottom walls; a layer of fiber material encapsulates the cores and bridges the adjacent edges of said end, side, and bottom walls; and a cured resin material saturates said layer of fiber material to form a unitary composite box structure.
The composite box also includes fiber material caps along the length of said core, side-by-side positioning of said cores, and resin saturated fiber material form I beam reinforcements in said end, side, and bottom walls and said top.
The composite box can be constructed with a co-molded layer molded to the top and side and bottom walls. The co-molded outer surface would protect against UV degradation and weathering, and therefore will have enhanced UV stability and enhanced abrasion, impact, and wear resistance. The co-molded layer can be either a film or sheet of material which will bond chemically and/or mechanically with the resin system used in fusing the composite portion of the box. Co-molded layer could be, inter alia, a sheet made of acrylic or polyvinylidene fluoride. The co-molded surface should, in addition, guard against fiber print-through and offer an aesthetically pleasing surface with multiple color options, which should not fade over the expected product life.
A railroad car may be built comprising a box, as defined above, mounted to a wheeled frame structure reinforced with steel I beams that interact with the I beam reinforcements in said bottom wall. The composite box can also be used for cargo and shipping containers, truck trailer bodies, modular housing, and insulated refrigeration rail cars.